Housekeeping of Python client repository (#103)

After working on reproducible package proparation for Python client
it's been found that the Python client repository had some extra
code added and docs and tests were placed in a wrong directory.

As of #93, we
have duplicated airflow_client code:

* airflow_client.client - this is the one that should be used
* airflow_client.airflow_client - this is the one that is added
  accidentally (and it is a copy of the `client` one)

Also `docs` and `tests` are generated in "airflow_client" package,
but this is wrong, both docs and tests should be at the top-level
of the repository.

This PR:

* deletes the extra code
* moves "docs" and "test" folders to the top-level of the project.

Author: potiuk

.github/workflows/ci.yml

@@ -37,4 +37,6 @@ jobs:
       - name: Run pytest
         run: |
           pip install -r test-requirements.txt
-          pytest airflow_client/test
+          pytest test
+        env:
+          PYTEST_ADDOPTS: "--color=yes"